Hydraulic binding compounds and method of producing the same



EXAMINER June 4, 1957 G. WALTER l HYDRAULIC BINDING conpouuns Ann limonoF Paonucmc ma sus Filed April 25. 1952.

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United States Patent O HYDRAULIC BINDING COMPOUNDS AND NIETHOD FPRODUCING THE SAME Georges Walter, Perroy, Switzerland Application April25, 1952, Serial No. 284,286 18 Claims. (Cl. 106-97) The presentinvention relates to the production of hydraulic binding compounds, andis particularly directed to the production of a rapid hardeninghydraulic binding compound having high initial and nal strength,especially 'with respect to resistance to bending stresses, thisapplication being a continuation-in-part of my co-pending applicationSerial No. 9,137, tiled February 18, 1948, now abandoned.

The primary object pf the present invention is to produce a rapidhardening hydraulic binding compound having high initial and finalstrength, especially with respect to resistance to bending stresses, andcapable of withstanding any atmospheric conditions to which it may beexposed for indefinite periods of time without exhibiting anyunsoundness or volume expansions of the order causing cracks ordisintegration.

The tendency in cement manufacture has been to progressively increasethe neness of the particles so that, while in 1886 a residue of percenton a sieve having 50 meshes per linear inch was not consideredunreasonable, at present the normal cements are usually ground tospecifications leaving a residue of 5 percent on a 170 mesh sieve andthe rapid hardening cements to speciiications leaving a residue of only1 to 3 percent on the same 170 mesh sieve. Cements ground in accordancewith these existing standards will hereinafter be referred to as finelyground cements. In using these known cements in producing concrete, highstrength has been sought by increasing the proportion of the finelyground cement in the mixture. However, it has been found that there isan optimum proportion of cement that may be included in the mixture,usually between 600 and 800 kilograms per cubic meter, and exceedingthis optimum proportion results in a decrease in the resistance orstrength of the concrete. This decrease in resistance results from theheat and shrinkage produced by the gel developed at the surfaces of thecement grains. If the proportion of cement in the mixture is increasedby the addition of finely ground particles or grains, the total surfacearea of the cement included in the mixture is increased and a quantityof gel is developed which produces excessive heat and shrinkage. Thus,the proportion of cement in the mixture may be increased beyond theabove indicated optimum values to provide increased strength only ifsuch increases do not excessively increase the total surface area of thecement grains and produce undesirable heat and shrinkage. It is apparentthat the proportion of cement in the mixture may be increased withoutexcessively increasing the total surface area of the cement grains byproviding a cement which includes relatively large particles in additionto the now conventional finely ground cement grains.

However, the addition of relatively large particles to the finely groundcement grains raises a threat to the soundness or stability of theconcerete which is much greater than the danger posed by theaforementioned development of heat and resultant shrinkage. This threatto the soundness or stability/of the concrete arises from 2,794,748Patented June 4, 1957 the action of calcium oxide or lime contained, ingreater or lesser degree, within the relatively large particles. In thecase of the very finely divided cement grains, any lime present in theclinkers from which the grains are ground will appear at the outersurfaces of the grains, the grains being sniciently small so that nointernal pockets may remain, and, therefore, the lime hydrates rapidlyand the expansion or swelling produced by such hydration is completedbefore settling occurs. ln the case of relatively large grains orparticles of cement, the grains will be more or less porous and willcontain more or less lime or calcium oxide some of which may be locatedin internal pockets of the particles, depending upon the size thereofand the properties of the clinker from which the large grains areformed. Thus, if the original clinker is extremely pgrgus anggntains,substantial quantities of lime, relatively large grains or particlesformed from such clinker will include internal pores or intersticescontaining substantial deposits of lime, and the hydration of this limewill proceed slowly and will continue to occur after the setting of theconcrete has been completed thereby causing swelling and subsequentcracking or disintegration of the concrete.

Accordingly, it is an object of the present invention to provide amethod for the production of a rapid hardening hydraulic binder havinghigh initial and tinal strength, particularly with respect to itsresistance to bending stresses, and made up of relatively largeparticles in addition to the conventional finely ground cement, whereinprocedures are included for ensuring that the relatively large particleswill not result in unsoundness by reason of the hydration of limecontained therein after setting of the binder has been completed.

ln accordance with the present invention, an hydraulic binder for use inpreparing concrete having a high resistance, particularly to bending, isproduced by grinding a quantity of clinker to provide a nely dividedcement, separately grinding more of the same clinker to providerelatively large particles having various sizes exceeding the sizes ofthe grains in the finely divided cement, passing the relatively largeparticles through sieves having openings of successively decreasing sizeto obtain segregated groups of relatively large particles havingdiierent size ranges, subjecting each of the groups of large particlesto immersion in boiling water for a period of 200 hours, and mixing withcement formed from the same, or from similar, clinker relatively largeparticles formed from the same clinker and of the size range of thatgroup which withstood the immersion in boiling water for 200 hourswithout exhibiting 4any unsoundness.

In the following description of specific embodiments of the presentinvention reference is to be had to the accompanying drawing wherein:

Fig. 1 is a diagrammatic representation of the arrangement of particlesin an hydraulic binder produced in accordance with the conceptsrecognized as standard prior to the present invention;

Fig. 2 is a diagrammatic representation, similar to Fig. l, but showingthe arrangement of particles in an hydraulic binder produced inaccordance with the present invention;

Fig. 3 is a side elevational view of a device that may be used inconnection with a method embodying the present invention;

Fig. 4 is a horizontal sectional view taken device of Fig. 3; and

Fig. 5 is a graphic representation showing the extent of the swelling ofvariously sized particles.

As previously indicated, increasing the resistance to bending of mortarsor concretes requires the increase of the proportion of cement in themixture beyond the values which are now considered optimal. If theproportion of ICC through the finely ground cement particles conformingto the existing standards, that is, particles ground to a neness so thatless than 5 percent remains on a 170 mesh sieve, is increased above thepresently recognized optimal values of 600 to 800 kilograms per cubicmeter, the total surface area of the cement particles increases to suchan extent that the gel developed at the surface produces excessive heatand shrinkage. However, if the proportion of cement in the mixture isincreased by substituting relatively large cement particles for some ofthe finely ground particles, the total surface area of the particleswill be reduced and excessive heating and shrinkage will be avoided.Referring to Fig. l, it will be seen that the small particles a have arelatively great surface area at which large quantities of gel e may beproduced. When certain of the small particles a of Fig. l are replacedby relatively large particles A, as in Fig. 2, the proportion of cementin the mixture can be increased, and the total surface area of thecement particles is maintained at an acceptable value so that only smallquantities of gel e are developed.

Thus, in providing an hydraulic binder having improved strength,particularly with respect to its resistance to bending stresses, it isessential first of all to recognize that the presently accepted optimumvalues for the proportion of cement in the mixture must be exceededwhile avoiding excessive heating and shrinkage due to the development ofgel and that these conditions may be satisfied by using relatively largeparticles as part of the cement. Further, such a cement must include, inaddition to the relatively large particles, a substantial proportion offinely ground cement, ground according to existing specifications, inorder to provide the desired rapid hardening properties and freedom frombleeding Certain tests have heretofore been employed in determining orforecasting the soundness of cements which are finely ground inaccordance with existing specifications. The most widely used of thesetests are the Le Chatelier test and the hot pat" test.

In the Le Chatelier test, the gauged cement is poured into alongitudinally split tube or cylinder provided with two needles whichdiverge as the cylinder is forced open by the swelling or expansion ofthe material contained therein. After the cylinder has been filled, itis immersed in water at 15 centigrade for twenty-four hours to completethe setting of the cement. The distance between the needles is thenmeasured and the cylinder replaced in cold water which is brought to 100centigrade within half an hour and is then kept boiling for three hours.Previously, the boiling was continued for six hours, but the presentpractice is to reduce the period to the extent indicated above. Aftercooling, the distance between the two needles is again measured, and thedifference between the lirst measurement and the last mentionedmeasurement represents the expansion or swelling of the cement.According to accepted standards this difference must not exceed mm. whenfirst tested, and if this value is exceeded the cement may be spread outand aerated for seven days, after which the expansion must not exceed 5mm.

In the hot pat test, the cement is gauged to a plastic paste and formedon a glass plate into pats about 3 inches in diameter and l inch thickat the center and tapering to a thin edge. The pats are kept in a moistatmosphere for 24 hours and then heated in steam at 100 centigrade orboiling water for 3 to 5 hours. Unsoundness is shown by the appearanceof distortion, cracking or disintegration.

In determining the soundness or unsoundness of finely ground cements,the above described tests are adequate. Since the particles are all verysmall in size, any lime contained in the cement will appear at thesurface of the particles and will not be contained in pores orinterstices within the particles. Thus, the accelerated tests, describedabove, will produce the hydration of the exposed lime during therespective short periods of 3 hours or 3 to 5 hours and any expansion orswelling will be completed during those periods.

However, I have found that certain cements containing finely groundparticles, in accordance with existing specifications, and relativelylarge particles added thereto will, when subjected to the Le Chatelieror hot pat" tests, appear to be sound, but will nevertheless crack anddisintegrate when subjected to adverse atmospheric conditions forextended periods. Such delayed cracking or disintegration results fromthe expansion or swelling produced by hydration of the lime contained inthe pores or interstices within the relatively large particles. The limein such pores or interstices is not affected by the boiling for 3 to 5hours, as in the above described tests, and, therefore, such tests areunreliable in determining the soundness of cements including largeparticles.

If cements are to be produced having relatively large particles thereinto achieve improved resistance, particularly to bending, it is apparentthat such cements, to be of any value, must be sound and capable ofwithstanding exposure to adverse atmospheric conditions for indefiniteperiods. Thus, the large particles added to thc finely ground cementmust not have quantities of occluded lime sufficient to causeunsoundness over such indefinite periods. l have found that the quantityof occluded lime, or lime contained in pores or interstices, in therelatively large particles will depend upon the properties of theclinker from which such large particles are produced and the size of therelatively large particles. Thus, if the clinker is porous, asdistinguished from compact, and contains excessive quantities of lime,it is probable that relatively large particles formed from that clinkerwill have pores therein containing lime which will produce expansionafter setting. The lime contained in such pores may be exposed byfurther breaking down the large particles until the resulting particlesare substantially compact. When the clinker used is substantially porousand contains relatively large deposits of lime, the usable particles,while larger than the grains in finely ground cement, cannot be as largeas the usable particles that are formed from compact and relatively limefree clinker.

Since it is desirable to employ the largest particles that may be usedfrom a particular clinker or batch of clinkers having the samecharacteristics without resulting in unsoundness, the present inventionprovides a process for producing a rapid hardening hydraulic binderhaving improved resistance, particularly to bending, which includesadding relatively large particles to finely ground cement andestablishes procedures permitting the addition of the largest possibleparticles while ensuring against the occurrence of unsoundness by reasonof the action of lime trapped within the large particles. In accordancewith the present invention, and contrary to the accepted view that atreatment in boiling water for 3 to 5 hours o without the appearance ofexcessive expansion, distortion,

cracking or disintegration, as in the Le Chatelier or hot pat tests,proves the soundness of a cement, l have found that these short testperiods are wholly inadequate to indicate the unsoundness of particleswhich are substantially coarser than the usual finely groundrapid-hardening cements, and that a reliable and safe indication of thesoundness of such large or coarse particles is obtained only when thetest period is increased drastically to endure for 10 to 16 or moretimes the period heretofore considered suitable.

By way of example, a number of test bars were made up. One test bar wascomposed entirely of a finely ground cement that was indicated to besound by the conventional hot pat test. The remaining test bars wereformed of equal parts of the sound finely ground cement and ofrelatively large grains ranging in size from 0.088 mm. up to 15.0 mm.and formed from the same or similar clinkers used in producing thefinely ground cement. That is, one of the composite bars includedrelatively large particles ranging in size from 0.08 mm.

to 0.13 mm., another bar had relatively large particles ranging in sizefrom 0.13 mm. to 0.20 mm., and so forth in suitable steps up to 15.0 mm.These test bars were exposed for 24 hours to moist air to permit settingand then immersed in a bath of water which was brought to a boil in amanner similar to the hot pat test. After S hours of boiling, all of thebars were intact and exhibited no distortion or cracking. The boilingwas then continued up to 200 hours, with observations being made at 6hour intervals. It was found that the bar having the largest particlesincluded therein cracked after 48 hours and all of the bars containingparticles larger than 1.0 mm. cracked or disintegrated by the end of 100hours. Between the 100th and 200th hours no further changes wereobserved thereby indicating that cement containing relatively largeparticles no greater than 1.0 mm., for example, particles ranging insize from 0.2 to 1.0 mm., would be sound for indefinite periods.

Repeating the above procedure with finely ground cement and relativelylarge particles of varying sizes formed from different clinkers, it wasfound that the maximum size of relatively large particles usable withoutproducing failure during the 200 hour boiling period varied for thedifferent clinkers. Using the information obtained as indicated abovesample concrete structures were fabricated for each of the clinkers usedin the experiments and formed of finely ground cement, finely groundcement and large particles of sizes indicated to be sound, and finelyground cement and large particles of sizes indicated to be unsound. Itwas found that the concrete structures formed of the finely groundcement combined with the relatively large particles indicated to besound exhibited bending and compressive strengths far exceeding thecorresponding characteristics of the concrete structure formed of thefinely ground cement alone. Further, after 61/2 years of exposure to theatmosphere, the sample concrete structures formed of nely ground cementcombined with relatively large particles indicated to be sound have inno case exhibited any signs of unsoundness, while the correspondingsample structures including large particles indicated to be unsoundhave, over the same period, disclosed cracks and other signs ofunsoundness.

particles having various sizes exceeding the sizes of the grains in thefinely divided cement, segregating the relatively large particles toobtain groups of relatively large particles having different sizeranges, subjecting the finely ground cement and each of the groups oflarge particles to a medium enhancing the swelling thereof for a periodsufficient to effect the complete swelling of the particles, and mixingwith the finely ground cement relatively large particles formed from thesame or similar clinker and of the size range of that group whichexhibited no unsoundness during subjection to said medium.

As a specific example of the above method, I present the following:

Finely ground initial high resistance commercial cement and a quantityof clinkers, corresponding to that from which the cement was formed,were obtained from the same source. The clinkers were ground in aconventional ball mill until relatively large particles ranging in sizeup to 15.0 mm. were obtained. By passing the ground clinkers through aseries of sieves having progressively decreasing mesh openings, theground clinkers were segregated into seven groups of particles havingrespective ranges of sizes as follows: 0.08 to 0.13; 0.13 to 0.2;

0.2 to 0.45; 0.45 to 1.0; 1.0 to 3.0; 3.0 t0 8.0; and 8.0

to 15.0 mm.

Each of the segregated groups of relatively large particles was mixedwith nely ground cement, in the proportion of percent by weight ofcement and 50 percent by weight of the relatively large particles, andgypsum was added in quantities inversely proportional to the size of therelatively large particles, as shown on Table I below. Each mixture hadwater added thereto to obtain a plastic consistency.

Two prismatic test pieces were formed in molds for each of the abovemixtures and for the finely ground cement alone, and the dimensions ofeach test piece were 4 x 4 x 16 cm. The setting of the test piecesoccurred at normaltemperatures and humidity for a period of 24 hours.The test pieces were then immersed in water which was heated to boilingand the boiling continued for 200 hours. The results of this subjectionto boiling water for 200 hours are summarized below:

TABLE I Mixture Proportions, Cement to Particles, Percent By WeightAddition of Gypsum, Percent Sizes of the Particles, No' of PiecesObserved Results Particles All of these test pieces withstood theboiling for m0 hours without exhibiting any d1stortion, cracking orother signs of unsoundness.

One test piece showed slight cracks alter 96 hours and the other testpleoe showed slrnllar cracks after hours, and both test pieces weredlslntegrated after 200 hours.

Thus, it was established that the addition of relatively large particlesto the finely ground cement can produce an hydraulic binder havingimproved resistance, particularly to bending, and that, in producingsuch a binder, special procedures must be employed in providing largeparticles that will avoid unsoundness. Generally, the method or processaccording to one embodiment of the present invention for producing arapid hardening hydraulic binder having improved resistance,particularly to bending, includes the steps of grinding a particularclinker to provide finely divided cement in accordance with existingstandards, that is, leaving no more than 5 percent on a -mesh sieve,separately grinding more of the same or similar clinker to providerelatively large 75 days of aging, the hand shaken samples showedbindingY Having established that no unsoundness will result from theaddition of particles ranging in size up to 8.0 mm., such particles arethen mixed with the finely ground cement in sufficient quantity so thatthe relatively large particles constitute at least l5 percent by weightof the mixture. In specific examples of this mixture, relatively largeparticles were added to the finely ground cement so that the particleslarger than 0.2 mm. but smaller than 8.0 mm; represented 60 percent ofthe total mixture, with 56 percent of such particles having sizesranging between 1.0 and 3.0 mm. Such specific mixtures were then formedinto samples some of which were vibrated and some of which were merelyhand shaken into the molds. After 3 strengths of approximately 200lig/cm?, and the vibrated samples showed binding strengths ofapproximately 250 lig/cm?. After 7 days of aging, the hand shakensamples showed binding strengths of approximately 210 kg./cm.2, whilethe vibrated samples showed binding strengths of approximately 320lig/cm?. In compression, all of the samples withstood approximately 1000lig/cm?, after only 3 days of aging, and the vibrated samples, after 7days of aging, withstood compressive stresses of approximately 1300kg./cm."'.

While the samples were boiled for 200 hours in thc above describedmethod and showed no further changes after 100 hours, it is to be notedthat the boiling does not have to be continued for 200 hours in allcases. Thus, if the samples show no further changes after 60 hours, forexample, it will be sufficient to continue the boiling for an additional100 hours, that is, for a total period of 160 hours, in order to ensurea perfectly reliable indication of the soundness of the relatively largeparticles.

I have further found that an accelerated procedure may be employed fordetermining the maximum size of relatively large particles that can beadded to the finely ground cement without producing unsoundness. Inaccordance with this other embodiment of the invention, clinker isground to provide finely divided cement in accordance with existingstandards. More of the same clinker is separately ground to providerelatively' large particles of various sizes exceeding the sizes of thegrains in the finely ground cement. The relatively large particles arethen segregated to obtain groups of different size ranges and samplesare formed of the finely ground cement alone and of mixtures of the nelyground cement with each of the groups of relatively large particles.After the samples have set, their lengths are measured, and then thesamples are subjected to a medium enhancing the swelling thereof, forexample, boiling water, for a period of at least 48 hours. After thetermination of this period, all of the samples are again measured and itwill be noted that the samples containing progressively larger particlesup to a certain size expanded progressively less than the samplecontaining only the finely ground cement, and that the samplescontaining particles larger than the above mentioned certain sizeexpanded more than the sample containing only the finely ground cement.Finally, a rapid the boiling for 200 hours without measurement, aspreviously set forth.

As a specific example of the second described method of producing anhydraulic binder, I present the following:

Finely ground initial high resistance commercial cement and a quantityof clinkers, corresponding to that from which the cement was formed,were obtained from the same source. The clinkers were ground in aconventional ball mill until relatively large particles ranging in sizeup to 15.0 mm. were obtained. The large particles were segregated intosix groups having different ranges of sizes as follows: 0.20 to 0.45;0.45 to 1.0; 1.0 to 3.0; 3.0 to 6.0; 6.0 to 8.0; and 8.0 to 15,0. Suchsegregation was obtained by passing the large particles through a seriesof sieves having mesh openings of progressively decreasing sizes. Eachof the segregated groups of relatively large particles was mixed withfinely ground cement in equal proportions by weight, with gypsum beingadded in quantities decreasing substantially inversely with respect tothe increasing particle size. Water was then added to each mixture toobtain a plastic consistency.

Three prismatic test pieces were formed in molds for each of the abovedescn'bed mixtures and for the finely ground cement alone, and thedimensions of each test piece were 4 x 4 x 16 cm. The test pieces werepermitted to set for 24 hours at normal temperatures and humidity. Aftersetting, each test piece was stripped from its mold and placed in adevice of the kind shown in Figs. 3 and 4. Such device includes acontainer 1 for water 2 having radially extending ribs 8 formed withperforations 9 to position the test piece 3 at the Center of thecontainer. A pivoted feeler 5 is mounted above container 1 and engagesthe top of the test piece. The feeler 5 may have a gear segment thereonmeshing with a gear holding a pointer 6 which cooperates with acalibrated scale 7 to indicate expansion of the test piece, After thetest pieces are placed in the above described devices, the readings ofthe pointers 6 on scales 7 are noted, and the water in the containers isbrought to a boil by suitable heaters (not shown). The boiling continuesfor at least 48 hours and the scale indications are recorded for atleast the 18th and 48th hours.

The results of the above described steps are summarized as follows:

TABLE II Expansion After 18 Expanslon After 48 Hours Hours Mixture Sizesof Particle and Percent` By Weight Test Piece Average Test Piece Averagexpanslon Elxlpanslon (Microns) ferons) 1 2 3 l. 2 3

60 40 50 50 60 50 53 20 30 30 27 20 30 40 30 30 m 30 27 30 20 40 30 l010 20 13 20 Z0 30 23 Z) 30 30 27 30 110 50 l 63 Z) 30 11 20 70 40 50 l53 30 40 ZJ 30 50 30 l (7) l Without distortion, crackin l With crackingand disintegration visible to the naked eye.

sizes of the relatively large particles as determined by g ordisintegration visible to the naked eye.

The recordings set forth in Table II are presented graphically in Fig. 5wherein the ordinates are the expansion readings and the abscissasrepresent the sizes of the particles. Line 1 represents the expansion ofthe test pieces after 18 hours and line 2 represents the expansion ofthe same test pieces after 48 hours. Line 3 represents the expansion ofthe test pieces containing relatively large particles as compared withthe expansion of the test pieces formed only of the finely groundcement, and having no particles or grains larger than 0.08 mm., after 18hours, while line 4 shows the same comparison after 48 hours.

In accordance with the second embodiment of the invention, the particleswhich, when added to the finely ground cement, will not result inunsoundness, are those which did not swell or expand more than thecement alone.

From the results summarized above, it follows that a sound hydraulicbinder having improved resistance, particularly to bending, may beprovided in accordance with the invention by adding relatively largeparticles, up to sizes of less than 6.0 mm., to the finely groundcement.

While the foregoing examples have added the relatively large particlesto finely ground cement made from the same clinker, it should be notedthat the finely ground cement may be formed from other clinker so longas the cement is sound.x But in this case the accelerated boiling testfor a period of 48 hours cannot be performed exactly as hereinbeforedescribed. Specifically, the largest particles which c'ienrbe safelyused are those of a size corresponding to a minimum value of theobtained curve, for beyond that size the swelling increases indefinitelyand not in comparison with the finely ground cement. Further, thedimensions given for the test pieces are not critical. Numerousempirical tests have shown that the above described comparative methodof determining the largest particles safely included in the mixturegreatly decreases the time required for effecting such a determination,and serves to indicate, in the shortened period, the upper limit of theparticle size which would be capable of withstanding the boiling testfor a period of 200 hours without exhibiting unsoundness and in this waythe definitive soundness of the resulting concrete.

Another method of producing an hydraulic binder having improvedresistance, particularly to bending, requires, as before, the provisionof finely ground cement and segregated groups of relatively largeparticles having different size ranges and produced from the same orsimilar clinker. A test piece is then prepared from a mixture of thenely ground cement and particles having the full range of sizes includedin all of the groups. If this test piece proves to be unsound whensubmitted to the boiling test for 200 hours, then another test piece isprepared from a mixture of the finely ground cement and all of thegroups of the relatively large particles with the exception of thatgroup having the largest particles. 'I'his second test piece is thensubjected to the boiling test. If the second test piece fails then athird test piece, omitting the next largest group of relatively largeparticles, is prepared. This step-by-step process continues until themaximum particle size which will be indefinitely sound has beendetermined.

While the times given for the various tests described above arepreferable when employing boiling water as the medium enhancing theswelling of the test pieces, these times may be shortened by a treatmentat temperatures higher than 100 centgrade, as with steam or boilingwater under an increased pressure. In any event, the duration of thetreatment will be such that further treatment produces no further changein the test pieces, and the required duration will vary as a function ofthe temperature and pressure. When the temperature and pressure areincreased, thetime of setting of the test pieces may be increased beyondthe conventional 24 hours.

Since the size of the relative large particles that may be safely addedto the cement without producing unsoundness varies depending upon theporosity and lime content of the clinkers from which such particles areformed, it is apparent that certain clinkers, which are extremely porousand contain or form too much lime, must be ground to the size of finelyground cement, that is, grains smaller than 0.08 mm. to avoidunsoundness. Such undesirable clinkers will be usable, if at all, in

1But ln this case the accelerated boiling test for 48 hours can not beerformed exactly as heretnbefore described. The large partie es can thenbe used until the size corresponding to a minimum of the obtained curveafter which the swelling increases indefinitely, and not in comparisonwith the nely ground cement.

forming the relatively large particles to be added to the finely groundcement, only after the burning of the clinkers is intensified slightlyabove normal without producing a harmful degree of vitrification.

However, in all cases I have found that the sizes of the large particlesthat may be added without producing unsoundness will be increased, toenhance the improvement in the bending strength of concretes or neatcements formed therefrom, by preparing the clinkers to be used for therelatively large particles in the manner hereinafter set forth.

For finely ground cement, it is sufficient that the clinker removed fromthe rotary furnace have an apparent density of 2.55 to 2.65, while theactual density of this material is approximately 3.1. The differencebetween the apparent and actual densities results from the numerouspores which are enclosed within the compact parts of the clinkers. Whenthe clinker is finely ground, none of the resulting grains are largeenough to enclose any of such pores and any lime contained in the poresis exposed and substantially hydrated during the grinding operation.When the clinker is only roughly crushed to produce the relatively largeor coarse particles, the various pores are not all broken through, andlime contained or formed later in such pores can become the center ofsubsequent destructive expansion. Accordingly, it is preferable that theclinker, employed in connection with the present invention, be baked ina manner to provide larger compact areas, between the pores that may beincluded therein, than those previously considered necessary in theproduction of finely ground cement. This may be achieved by increasingthe baking or burning period or by the addition of any suitable uxingagents, which are well known, or by a combination of the two. Byemploying these procedures, clinkers may be obtained at the outlet ofthe furnace having apparent densities exceeding 2.65.

Further, when the clinker is crushed in order to form the coarse orrelatively large particles, the apparent density may be furtherincreased by a prolonged treatment in a ball mill using relativelylittle balls so that the compact pieces are not broken up which therelatively porous portions of the clinkers are broken down and separatedfrom the compact pieces. The apparent density of the relatively largeparticles obtained in this manner may be elevated to the desired valueof at least 2.90.

Using large particles prepared as above and the methods previouslydescribed for determining the maximum size that may be added to thefinely ground cement without producing unsoundness, the maximumadvantages of the present invention may be achieved.

It goes without saying that, if the maximum resistance to bendingobtainable in the above described manner exceeds the practicalrequirements of a particular application, it may be more economical touse relatively large particles which are smaller than the maximumpermissible size indicated by the testing of the samples.

The proportions of the relatively large particles added to the finelyground cement are in accordance with the rules which are well known toworkers in the art for -forrning compact mortars and concretes. That is,the greater the difference between the sizes of the largest addedparticles and the grains of the finely ground concrete, the greater thequantity of relatively large particles that are added; and the smallerthe above mentioned difference, the smaller is the quantity that isadded. However, in order to produce any appreciable increase in theresistance to bending, it is necessary that the relatively largeparticles be greater than .2 mm., and that the quantity of suchparticles added form at least l5 percent of the total weight of themixture. In order to obtain maximal strength in bending, the addedrelatively large particles should include particles of 1.0 or moremillimeters and, in certain cases, as much as 10.0 mm.

An hydraulic binder produced in the manner described above may becomposed of finely ground Portland clinker and coarsely ground Portlandclinker, or in certain cases of finely ground aluminous clinker mixedwith coarsely ground aluminous clinker. Further, the hydraulic bindermay be formed of nely ground particles and relatively large particlesproduced from Portland clinker along with relatively large particlesproduced from aluminous clinker, and in such a case the surface area ofthe aluminous particles must be less than 10 percent, and preferablyless than percent, of the total active surface area of the entiremixture to provide the desired rate of setting. The setting time of themixtures formed entirely of finely ground and relatively large particlesformed from Portland clinker is regulated by the addition of gypsum asis well known.

Further, the bending strength is enhanced, in accordance with thepresent invention, by removing needles or splinters from and roundingthe edges of the relatively large particles added to the finely groundcement. The large particles should in no case be spherical, but merelydevoid of sharp edges, and this may be achieved by treating theparticles, after they have been crushed to the desired size, in a ballmill having a weak or small charge of balls.

lt is apparent that the relatively large particles may be added to thefinely ground cement either at the plant or at the point of use.

While l have described various illustrative embodiments and examples ofthe present invention, it is to be understood that the invention is notlimited thereby and that various changes and modifications may beeffected therein without departing from the scope of the invention whichis intended to be defined in the appended claims.

What I claim is:

l. A method of producing a rapid-hardening hydraulic binder having ahigh resistance, particularly to bending, comprising crushing clnkersseparately to obtain finely ground cement and relatively largeparticles, segregating said relatively large particles into groups ofparticles having different size ranges, forming test pieces from thefinely ground cement alone and from mixtures each of which includes saidfinely ground cement and particles from a respective one of said groups,exposing the test pieces, after hardening, to a medium enhancing theexpansion thereof for a period sufficient to complete the expansionthereof, and adding to the finely ground cement relatively largeparticles at most as large as the largest particles in the largest ofsaid groups which withstood exposure to said medium without exhibitingdistortion and cracking.

2. The method of making a cementitious product possessing the propertiesof rapid-hardening and high strength, particularly with respect tobending; comprising grinding cement clinker material to the normalfineness of finished cement alone so that less than 5 percent wouldremain on a 170 mesh sieve, separately grinding cement clinker materialto materially coarser sizes than the first mentioned ground material andhaving as their upper limit sizes which are capable, after hardening for24 hours at room temperatures and atmospheric pressures, of withstandingexposure to boiling water for 200 hours at atmospheric pressure withoutexhibiting distortion and cracking, and intimately mixing the coarsercement material made up of particles at most as large as the greatestsize particles withstanding the boiling water for 200 hours withoutexhibiting distortion and cracking with the cement material ground tothe fineness of nished cement.

3. The method according to claim 2 wherein said clinker material groundto the fneness of finished cement is Portland cement clinker and thecement clinker material ground to materially coarser sizes includesaluminous clnkers; the surface area of the coarser cement materialformed of said aluminous clnkers and added to the cement material groundto the neness of finished cement being less than percent of the totalsurface area of the mixture.

4. The method according to claim 2, including the step of rounding-olithe sharp edges of the particles of the coarser cement material prior tothe mixing thereof with the cement material ground to the fineness offinished cement.

5. The method according to claim 2, including adding gypsum to themixture in proportion to the surface area of the coarser cementlmaterial for controlling the setting time of the mixture.

6. The method of making a cementitious product possessing the propertiesof rapid-hardening and high strength, particularly with respect tobending; comprising grinding cement clinker to produce grains of thefineness of finished cement, separately crushing cement clinker todestroy the more porous parts thereof to the extent that the remainingcompact portions of the elinkers have an apparently density higher than2.90, grinding the compact portions to provide particles of materiallycoarser sizes than said grains, segregating said particles of materiallycoarser sizes into groups of particles having different size ranges,forming test pieces from the finely ground cement and from mixtures eachof which includes particles from a respective one of said groups,exposing said test pieces after hardening to boiling water for a periodof 200 hours, and intimately mixing said finely ground grains with thoseparticles of materially coarser sizes having an upper limitcorresponding at most to the sizes of the largest particles included inthe test pieces which withstood exposure to the boiling water withoutexhibiting distortion and cracking.

7. The method according to claim 6, including adding at least onefluxing agent to the clinker ground to produce the particles ofmaterially coarser sizes during the baking thereof.

8. A method of producing a rapid hardening hydraulic binder having ahigh resistance, particularly to bending, comprising crushing clinkersseparately to obtain finely ground cement and relatively largeparticles, segregating said relatively large particles into groups ofparticles having different size ranges, forming test pieces from thefinely ground cement alone and from mixtures each of which includes saidnely ground cement and particles from a respective one of said groups,exposing the test pieces, after hardening, to boiling water for 200hours, and adding to the finely ground cement relatively large particlesat most as large as the largest particles in the largest of said groupswhich withstood exposure to the boiling water for 200 hours Withoutexhibiting distortion and cracking.

9. A method of producing a rapid-hardening hydraulic binder having ahigh resistance, particularly to bending, comprising separately crushingclinkers to obtain finely ground cement and relatively large particles,segregating said relatively large particles into groups of particleshaving different size ranges, forming test pieces from the finely groundcement alone and from mixtures each including particles from arespective one of said groups, exposing the test pieces, afterhardening, to a medium enhancing the expansion thereof for a periodsufcient to produce hydration of any lime contained in the interior ofthe relatively large particles, measuring the expansion of said testpieces during exposure to said medium, selecting those test pieces whichthe measurements show to expand as little as the test pieces formed ofthe finely ground cement alone, and adding particles at most as large asthose included in the selected test pieces to the finely ground cement.

10. A method of producing a rapid-hardening hydraulic binder having highresistance, particularly to bending, comprising separately crushingclnkers to obtain finely ground cement and relatively large particles,segregating said relatively large particles into groups of particleshaving different size ranges, forming test pieces from the nely groundcement alone and from mixtures each including particles from arespective one of said groups,

exposing the test pieces, after hardening, to boiling water for a periodof at least 48 hours, measuring the expansion of said test pieces duringexposure to said medium, selecting those test pieces which themeasurements show to expand as little as the test pieces formed of thefinely ground cement alone, and adding particles at most as large asthose included in the selected test pieces to the nely ground cement.

l1. A method according to claim 10, wherein said relatively largeparticles added to the linely ground cement have dimensions of 0.2 to3.0 mm.

12. A method according to claim 1l, wherein the quantity of relativelylarge particles added to the finely ground cement is at least 15 percentby weight of the combined weight of the relatively large particles andthe finely ground cement.

13. The method of making a cementitious product possessing theproperties of rapid-hardening and high strength, particularly withrespect to bending; comprising separately crushing clinkers to obtainfinely ground cement less than 0.2 mm. and relatively large particles,segregating said relatively large particles into groups of particleshaving different size ranges, forming test pieces from the finely groundcement and from mixtures each of which includes particles from arespective one of said groups, exposing said test pieces to theatmosphere for 24 hours to permit the hardening thereof, exposing thehardened samples to boiling water at atmospheric pressure for a periodof at least 48 hours, measuring the expansion of said test pieces duringexposure to said medium, selecting those test pieces which themeasurements show to expand as little as the test pieces formed of thefinely ground cement alone, and adding particles at most as large asthose included in the selected test pieces to the inely ground cement.

14. The method of making a cementitious product possessing theproperties of rapid-hardening and high strength, particularly withrespect to bending; comprising separately crushing clinkers to obtainnely ground cement and relatively large particles, segregating saidrelatively large particles into groups of particles having differentsize ranges, forming test pieces from the finely ground cement alone,and from mixtures each of which includes particles from a respective oneof said groups, exposing said test pieces after hardening to a moistmedium under pressure and at a temperature greater than 100 centigradeenhancing the expansion of said test pieces for a period sucient tocomplete the expansion of the test pieces, measuring the expansion of .o

said test pieces during exposure to said medium, selecting those testpieces which the measurements show to expand as little as the testpieces formed of the nely ground cement alone, and adding particles atmost as large as those included in the selected test pieces to thefinely ground cement.

15. The method of making cementitious product possessing the propertiesof rapid-hardening and high strength, particularly with respect tobending; comprising grinding cement clinker material to the tineness ofnished cement, separately grinding cement clinker material to amaterially coarser size than the first mentioned ground material,forming a test piece prepared from mixture of the finally ground cementand coarser particles having the full range of sizes, and another testpiece containing nely ground cement and coarser particles having thefull range of sizes minus the largest particles contained in the rstnamed test piece and so on step by step up to the less large particlesof the considered coarser grains, submitting after hardening lthechoiced series of test pieces to boiling water for 200 hoursestablishing which test pieces remain without distortion or cracking;mixing finely ground cement with the full range of coarser particles ofwhich the maximum particles size corresponds at most at the maximum sizeincluded in the test piece containing the largest grains havingwithstood said test without exhibiting distortion or cracking.

16. A method according to claim 1, wherein the quantity of relativelylarge particles added to the nely ground cement is at least 15 percentby weight of the combined weight of the finely ground cement and therelatively large particles.

17. A method according to claim 2, wherein the relatively largeparticles added to the finely ground cement are greater than 0.2 mm. insize.

18. A method according to claim 1, wherein the grains of the finelyground cement have sizes ranging up to maximum 0.08 mm.

References Cited in the le of this patent FOREIGN PATENTS 653,839 GreatBritain Oct. 12, 1951 242,119 Switzerland Apr. 30, 1946 653,839Switzerland Oct. 12, 1951 OTHER REFERENCES Lea and Desch: The Chemistryof Cement and Concrete (1935), pp. 218-219.

2. THE METHOD OF MAKING A CEMENTITIOUS PRODUCT POSSESSING THE PROPERTIESOF RAPID-HARDENING AND HIGHSTRENGTH, PARTICULARLY WITH RESPECT TOBENDING; COMPRISING GRINDING CEMENT CLINKER MATERIAL TO THE NORMALFINENESS OF FINSIHED CEMENT ALONE SO THAT LESS THAN 5 PERCENT WOULDREMAIN ON A 170 MESH SIEVE, SEPARATELY GRINDING CEMENT CLINKER MATERIALTO MATERIALLY COARSER SIZES THAN THE FIRST MENTIONED GROUND MATERIAL ANDHAVING AS THEIR UPPER LIMIT SIZES WHICH ARE CAPABLE, AFTER HARDENING FOR24 HOURS AT ROOM TEMPERATURES AND ATMOSPHERIC PRESSURES, OF WITHSTANDINGEXPOSURE TO BOILING WATER FOR 200 HOURS AT ATMOSPHERIC PRESSURE WITHOUTEXHIBITING DISTORTION AND CRACKING, AND INTIMATELY MIXING THE COARSERCEMENT MATERIAL MADE UP OF PARTICLES AT MOST AS LARGE AS THE GREATESTSIZE PARTICLES WITHSTANDING THE BOILING WATER FOR 200 HOURS WITHOUTEXHIBITION DISTORTION AND CRACKING WITH THE CEMENT MATERIAL GROUND TOTHE FINENESS OF FINISHED CEMENT.